This research proposal is based on the premise that the structure (crystallite size, morphology, internal strain, strength of bonding) and composition of the inorganic phase of dental enamel (which is principally an apatite) have jointly fundamental (although not exclusive) roles in the tooth's caries susceptibility or resistance. The immediate objectives of this study are: (1) to characterize dental enamel from different species of teeth according to their crystallographic properties and composition; (2) to characterize dental enamel (human) as function of age; (3) to characterize dental enamel from teeth obtained from areas of high cariostatic and high cariogenic 'trace elements'; (4) to determine the involvement of the trace elements in synthetic systems; (5) to define the structural and compositional factors relating to the caries susceptibility of human teeth. X-ray diffraction, infrared absorption spectroscopy, atomic absorption, electron microscopy will be used on the synthetic and biological apatites.